As is well known in the prior art, many cylinder locks include a plug (also called a tumbler) arranged for rotation in a body. The plug and body are provided with a number of bores in which plug pins and driver pins are disposed. The plug is formed with a keyway for inserting therein a key. The driver pins are aligned with the plug pins, and the plug and driver pins have varying lengths that define a key cut combination. Upon insertion of a key with the correct key cut combination, the faces of the plug pins and driver pins that touch each other are aligned flush with the circumferential surface of the plug, referred to as the shear line, and the plug may be rotated to actuate the lock. If the key cut combination is not correct, at least one of the driver and plug pins will cross over the shear line and prevent rotation of the plug, and thus prevent actuation of the lock.
The number of possible key cut combinations for such prior art cylinder locks depends only on the number of pins, the relative lengths of the plug and driver pins, and on the depths of the key cuts.